Final answer:
Newton's First Law, which is about inertia, explains why a book remains at rest on a shelf when undisturbed, as it states that an object will not change its state of motion without a net external force.
Step-by-step explanation:
The law demonstrated by a book that stays on the shelf all day after going unbothered is Newton's First Law, often referred to as the law of inertia. This law states that a body at rest will remain at rest, and a body in motion will continue in motion with a constant velocity, unless acted upon by a net external force. In the case of the book, it remains at rest on the shelf because there are no unbalanced forces causing it to move.